# Preface

## 0.1. The Unix Family of Operating Systems

An operating system (or "OS") is a set of programs that controls a computer. It controls both hardware (things you can touch, like keyboards, screens, and disk drives) and software (application programs that you run, like a word processor).

Some computers have a single-user OS, which means that only one person can use the computer at a time. Many older OSes (such as MS-DOS) can also do only one job at a time. But almost any computer can do a lot more if it has a multiuser, multitasking operating system such as Unix. These powerful OSes let many people use the computer at the same time and let each user run several jobs at once.

Unix was invented more than 30 years ago for scientific and professional users who wanted a very powerful and flexible OS. It's been significantly developed since then. Because Unix was designed for experts, it can be a bit overwhelming at first. But after you get the basics (from this book!) you'll start to appreciate some of the reasons to use Unix:

- It comes with a huge number of powerful application programs. You can get many others for free on the Internet. (The GNU utilities, available from the Free Software Foundation, are very popular.) You can thus do much more at a much lower cost.

- Not only are the applications often free, but some Unix versions are also free. Linux is a good example. Like the free applications, most free Unix versions are of excellent quality. They're maintained by volunteer programmers who want a powerful OS and are frustrated by the slow, bug-ridden OS development at some big software companies.

- Unlike OSes such as Microsoft Windows and MacOS that are designed for certain types of hardware, Unix runs on almost any kind, from tiny embedded systems to giant supercomputers. After you read this book, you'll be ready to use many kinds of computers without learning a new OS for each one.

- In general, Unix (especially without a windowing system) is less resource-intensive than other major operating systems. For instance, Linux will run happily on an old system with a x386 microprocessor and let multiple users share the same computer. (Don't bother trying to use the latest versions of Microsoft Windows on a system that's more than a few years old!) If you need a windowing system, Unix lets you choose from modern feature-rich interfaces as well as from simple ones that need much less system power. Anyone with limited resources--educational institutions, organizations in developing countries, and so on--can use Unix to do more with less.

- Much of the Internet's development was done on Unix systems. Many Internet web sites and Internet service providers use Unix because it's so flexible and inexpensive. With powerful hardware, Unix really shines.

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